The Long Trails, Series by Lizzi Tremayne

Escaping her father's killer, Aleksandra rode the Pony Express—full speed into the middle of the Indian Paiute Wars. Seventeen year old Aleksandra, trained in the Cossack arts from infancy by her father, finds herself alone and running to prevent her Pa's killer from obtaining a secret coveted by the Russian Czar, one which could alter the forces of power in Europe. Disguised as a Pony Express rider in 1860's Utah Territory, she finds herself in even deeper trouble... moreEscaping her father's killer, Aleksandra rode the Pony Express—full speed into the middle of the Indian Paiute Wars. Seventeen year old Aleksandra, trained in the Cossack arts from infancy by her father, finds herself alone and running to prevent her Pa's killer from obtaining a secret coveted by the Russian Czar, one which could alter the forces of power in Europe. Disguised as a Pony Express rider in 1860's Utah Territory, she finds herself in even deeper trouble. Her Californio boss Xavier has a strength to match her own, but can they overcome their differences before the ever-increasing odds overtake them? less